(Re-sent. Just found that my previous email seems not delivered to common-dev.)
> > The question is: how are we going to fix it?>> What do you propose? -C
First of all, let's state clearly what is the problem about. Please help me
out if I have missed anything.
The problem reported by HDFS-12990 is that HDFS-9427 has changed NN default RPC
port from 8020 to 9820. HDFS-12990 claimed, “the NN RPC port change is painful
for downstream on migrating to Hadoop 3.”
Note 1: This isn't a problem for HA cluster.Note 2: The port is configurable.
User can set it to any value.Note 3: HDFS-9427 has also changed many other
HTTP/RPC ports as shown below
Namenode ports: 50470 --> 9871, 50070 --> 9870, 8020 --> 9820Secondary NN
ports: 50091 --> 9869, 50090 --> 9868Datanode ports: 50020 --> 9867, 50010 -->
9866, 50475 --> 9865, 50075 --> 9864
The other port changes probably also affect downstream projects and give them a
“painful” experience. For example, NN UI and WebHDFS use a different port.
The problem is related convenience but not anything serious like a security bug.
There are a few possible solutions:1) Considered that the port changes are not
limited to NN RPC and the default port value should not be hardcoded. Also,
downstream projects probably need to fix other hardcoded ports (e.g. WebHDFS)
anyway. Let’s just keep all the port changes and document them clearly about
the changes (we may throw an exception if some applications try to connect to
the old ports.) In this way, 3.0.1 is compatible with 3.0.0.
2) Further change the NN RPC so that NN listens to both 8020 and 9820 by
default. It is a new feature that NN listen to two ports simultaneously. The
feature has other benefits, e.g. one of the ports is reserved to some high
priority applications so that it can have a better response time. It is
compatible to both 2.x and 3.0.0. Of course, users could choose to set it back
to one of the ports in the conf.
3) Revert the NN RPC port back to 8020. We need to ask where should the revert
happen?3.1) Revert it in 3.0.1 as proposed by HDFS-12990. However, this is an
incompatible change between dot releases 3.0.0 and 3.0.1 and it violates our
policy. Being compatible is very important. Users expect 3.0.0 and 3.0.1 are
compatible. How could we explain 3.0.0 and 3.0.1 are incompatible due to
convenience?3.2) Revert it in 4.0.0. There is no compatibility issue since
3.0.0 and 4.0.0 are allowed to have incompatible changes according to our
policy.
Since compatibility is more important than convenience, Solution #3.1 is
impermissible. For the remaining solutions, both #1 and #2 are fine to me.
Thanks.Tsz-Wo
On Friday, January 12, 2018, 12:26:47 PM GMT+8, Chris Douglas
<cdoug...@apache.org> wrote:
On Thu, Jan 11, 2018 at 6:34 PM Tsz Wo Sze <szets...@yahoo.com> wrote:
The question is: how are we going to fix it?
What do you propose? -C
> No incompatible changes are allowed between 3.0.0 and 3.0.1. Dot releases
> only allow bug fixes.
We may not like the statement above but it is our compatibility policy. We
should either follow the policy or revise it.
Some more questions:
- What if someone is already using 3.0.0 and has changed all the scripts to
9820? Just let them fail?
- Compared to 2.x, 3.0.0 has many incompatible changes. Are we going to have
other incompatible changes in the future minor and dot releases? What is the
criteria to decide which incompatible changes are allowed?
- I hate that we have prematurely released 3.0.0 and make 3.0.1 incompatible
to 3.0.0. If the "bug" is that serious, why not fixing it in 4.0.0 and declare
3.x as dead?
- It seems obvious that no one has seriously tested it so that the problem
is not uncovered until now. Are there bugs in our current release procedure?
ThanksTsz-Wo
On Thursday, January 11, 2018, 11:36:33 AM GMT+8, Chris Douglas
<cdoug...@apache.org> wrote:
Isn't this limited to reverting the 8020 -> 9820 change? -C
On Wed, Jan 10, 2018 at 6:13 PM Eric Yang <ey...@hortonworks.com> wrote:
> The fix in HDFS-9427 can potentially bring in new customers because less
> chance for new comer to encountering “port already in use” problem. If we
> make change according to HDFS-12990, then this incompatible change does not
> make incompatible change compatible. Other ports are not reverted
> according to HDFS-12990. User will encounter the bad taste in the mouth
> that HDFS-9427 attempt to solve. Please do consider both negative side
> effects of reverting as well as incompatible minor release change. Thanks
>
> Regards,
> Eric
>
> From: larry mccay <lmc...@apache.org>
> Date: Wednesday, January 10, 2018 at 10:53 AM
> To: Daryn Sharp <da...@oath.com>
> Cc: "Aaron T. Myers" <a...@apache.org>, Eric Yang <ey...@hortonworks.com>,
> Chris Douglas <cdoug...@apache.org>, Hadoop Common <
> common-dev@hadoop.apache.org>
> Subject: Re: When are incompatible changes acceptable (HDFS-12990)
>
> On Wed, Jan 10, 2018 at 1:34 PM, Daryn Sharp <da...@oath.com<mailto:
> da...@oath.com>> wrote:
>
> I fully agree the port changes should be reverted. Although
> "incompatible", the potential impact to existing 2.x deploys is huge. I'd
> rather inconvenience 3.0 deploys that compromise <1% customers. An
> incompatible change to revert an incompatible change is called
> compatibility.
>
> +1
>
>
>
>
> Most importantly, consider that there is no good upgrade path existing
> deploys, esp. large and/or multi-cluster environments. It’s only feasible
> for first-time deploys or simple single-cluster upgrades willing to take
> downtime. Let's consider a few reasons why:
>
>
>
> 1. RU is completely broken. Running jobs will fail. If MR on hdfs
> bundles the configs, there's no way to transparently coordinate the switch
> to the new bundle with the port changed. Job submissions will fail.
>
>
>
> 2. Users generally do not add the rpc port number to uris so unless their
> configs are updated they will contact the wrong port. Seamlessly
> coordinating the conf change without massive failures is impossible.
>
>
>
> 3. Even if client confs are updated, they will break in a multi-cluster
> env with NNs using different ports. Users/services will be forced to add
> the port. The cited hive "issue" is not a bug since it's the only way to
> work in a multi-port env.
>
>
>
> 4. Coordinating the port add/change of uris is systems everywhere (you
> know something will be missed), updating of confs, restarting all services,
> requiring customers to redeploy their workflows in sync with the NN
> upgrade, will cause mass disruption and downtime that will be unacceptable
> for production environments.
>
>
>
> This is a solution to a non-existent problem. Ports can be bound by
> multiple processes but only 1 can listen. Maybe multiple listeners is an
> issue for compute nodes but not responsibly managed service nodes. Ie. Who
> runs arbitrary services on the NNs that bind to random ports? Besides, the
> default port is and was ephemeral so it solved nothing.
>
>
>
> This either standardizes ports to a particular customer's ports or is a
> poorly thought out whim. In either case, the needs of the many outweigh
> the needs of the few/none (3.0 users). The only logical conclusion is
> revert. If a particular site wants to change default ports and deal with
> the massive fallout, they can explicitly change the ports themselves.
>
>
>
> Daryn
>
> On Tue, Jan 9, 2018 at 11:22 PM, Aaron T. Myers <a...@apache.org<mailto:
> a...@apache.org>> wrote:
> On Tue, Jan 9, 2018 at 3:15 PM, Eric Yang <ey...@hortonworks.com<mailto:
> ey...@hortonworks.com>> wrote:
>
> > While I agree the original port change was unnecessary, I don’t think
> > Hadoop NN port change is a bad thing.
> >
> > I worked for a Hadoop distro that NN RPC port was default to port 9000.
> > When we migrate from BigInsights to IOP and now to HDP, we have to move
> > customer Hive metadata to new NN RPC port. It only took one developer
> > (myself) to write the tool for the migration. The incurring workload is
> > not as bad as most people anticipated because Hadoop depends on
> > configuration file for referencing namenode. Most of the code can work
> > transparently. It helped to harden the downstream testing tools to be
> more
> > robust.
> >
>
> While there are of course ways to deal with this, the question really
> should be whether or not it's a desirable thing to do to our users.
>
>
> >
> > We will never know how many people are actively working on Hadoop 3.0.0.
> > Perhaps, couple hundred developers or thousands.
>
>
> You're right that we can't know for sure, but I strongly suspect that this
> is a substantial overestimate. Given how conservative Hadoop operators tend
> to be, I view it as exceptionally unlikely that many deployments have been
> created on or upgraded to Hadoop 3.0.0 since it was released less than a
> month ago.
>
> Further, I hope you'll agree that the number of
> users/developers/deployments/applications which are currently on Hadoop 2.x
> is *vastly* greater than anyone who might have jumped on Hadoop 3.0.0 so
> quickly. When all of those users upgrade to any 3.x version, they will
> encounter this needless incompatible change and be forced to work around
> it.
>
>
> > I think the switch back may have saved few developers work, but there
> > could be more people getting impacted at unexpected minor release change
> in
> > the future. I recommend keeping current values to avoid rule bending and
> > future frustrations.
> >
>
> That we allow this incompatible change now does not mean that we are
> categorically allowing more incompatible changes in the future. My point is
> that we should in all instances evaluate the merit of any incompatible
> change on a case-by-case basis. This is not an exceptional circumstance -
> we've made incompatible changes in the past when appropriate, e.g. breaking
> some clients to address a security issue. I and others believe that in this
> case the benefits greatly outweigh the downsides of changing this back to
> what it has always been.
>
> Best,
> Aaron
>
>
> >
> > Regards,
> > Eric
> >
> > On 1/9/18, 11:21 AM, "Chris Douglas" <cdoug...@apache.org<mailto:
> cdoug...@apache.org>> wrote:
> >
> > Particularly since 9820 isn't in the contiguous range of ports in
> > HDFS-9427, is there any value in this change?
> >
> > Let's change it back to prevent the disruption to users, but
> > downstream projects should treat this as a bug in their tests. Please
> > open JIRAs in affected projects. -C
> >
> >
> > On Tue, Jan 9, 2018 at 5:18 AM, larry mccay <lmc...@apache.org
> <mailto:lmc...@apache.org>> wrote:
> > > On Mon, Jan 8, 2018 at 11:28 PM, Aaron T. Myers <a...@apache.org
> <mailto:a...@apache.org>>
> > wrote:
> > >
> > >> Thanks a lot for the response, Larry. Comments inline.
> > >>
> > >> On Mon, Jan 8, 2018 at 6:44 PM, larry mccay <lmc...@apache.org
> <mailto:lmc...@apache.org>>
> > wrote:
> > >>
> > >>> Question...
> > >>>
> > >>> Can this be addressed in some way during or before upgrade that
> > allows it
> > >>> to only affect new installs?
> > >>> Even a config based workaround prior to upgrade might make this a
> > change
> > >>> less disruptive.
> > >>>
> > >>> If part of the upgrade process includes a step (maybe even a
> > script) to
> > >>> set the NN RPC port explicitly beforehand then it would allow
> > existing
> > >>> deployments and related clients to remain whole - otherwise it
> > will uptake
> > >>> the new default port.
> > >>>
> > >>
> > >> Perhaps something like this could be done, but I think there are
> > downsides
> > >> to anything like this. For example, I'm sure there are plenty of
> > >> applications written on top of Hadoop that have tests which
> > hard-code the
> > >> port number. Nothing we do in a setup script will help here. If we
> > don't
> > >> change the default port back to what it was, these tests will
> > likely all
> > >> have to be updated.
> > >>
> > >>
> > >
> > > I may not have made my point clear enough.
> > > What I meant to say is to fix the default port but direct folks to
> > > explicitly set the port they are using in a deployment (the current
> > > default) so that it doesn't change out from under them - unless
> they
> > are
> > > fine with it changing.
> > >
> > >
> > >>
> > >>> Meta note: we shouldn't be so pedantic about policy that we can't
> > back
> > >>> out something that is considered a bug or even mistake.
> > >>>
> > >>
> > >> This is my bigger point. Rigidly adhering to the compat guidelines
> > in this
> > >> instance helps almost no one, while hurting many folks.
> > >>
> > >> We basically made a mistake when we decided to change the default
> > NN port
> > >> with little upside, even between major versions. We discovered
> this
> > very
> > >> quickly, and we have an opportunity to fix it now and in so doing
> > likely
> > >> disrupt very, very few users and downstream applications. If we
> > don't
> > >> change it, we'll be causing difficulty for our users, downstream
> > >> developers, and ourselves, potentially for years.
> > >>
> > >
> > > Agreed.
> > >
> > >
> > >>
> > >> Best,
> > >> Aaron
> > >>
> >
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